This study has been designed to elucidate mechanisms by which neonatal chronic lung disease occurs and to test the capacity and safety of inhaled glucocorticoid to prevent the process of chronic lung disease and its accompanying effects on growth and development. This will be accomplished through a randomized, placebo controlled clinical trial of inhaled corticosteroid, beclomethasone dipropionate, in infants less than 1251 gm birth weight and less than 33 weeks gestation who, at 3 to 14 days of age, continue to require mechanical ventilation. Beclomethasone will be administered via manual ventilation with an anesthesia bag using a metered dose inhaler with a spacer device for a 28-day treatment period.